The bonding of metal surfaces to elastomeric substrates is an evolving art that requires continual advancement and modification of corresponding adhesive systems in order to cope with the rapidly changing automotive and industrial environments in which elastomer-metal assemblies are employed. Recent technological advances in automotive and industrial applications have resulted in relatively severe working environments for adhesively bonded elastomer and metal components. For example, many engine mounting devices that employ elastomer-metal adhesive bonds contain fluids in order to assist in damping of the vibration of the engine. These fluid-filled engine mounting devices are being exposed to increasingly high temperatures such that the elastomer-metal adhesive bonds within the mounts are being exposed to very high temperature fluid environments. In addition, many elastomer-metal assemblies, particularly those utilized in automobile applications, are routinely exposed to materials that contain corrosive salts or other corrosive materials that may act to degrade the elastomer-metal adhesive bond.
In order to effectively apply many of the currently available elastomer-metal adhesive compositions, it is necessary to pretreat the metal surface so as to remove any dirt, oil, moisture or weak oxide layers by utilizing one or more surface preparation techniques such as phosphatizing, alodizing, anodizing, solvent cleaning, grit blasting or vapor degreasing. Most adhesive compositions require that the metal surface be both degreased and grit-blasted before an adequate adhesive bond can be obtained. These techniques are relatively expensive, time-consuming, and some techniques may generate hazardous products such as chromates which create significant waste disposal problems. With increasing environmental awareness and the corresponding regulation of industry, the use of adhesive compositions which require substantial surface preparation will become increasingly expensive and cumbersome. It would, therefore, be desirable to create an adhesive composition that would eliminate the need for one or more of the above-mentioned metal surface preparation techniques.
Various adhesive compositions have previously been developed in an effort to improve elastomer-metal adhesion and coating technologies. For example, U.S. Pat. Nos. 3,258,388 and 3,258,389 disclose an adhesive composition containing a rubber adherent and a metal adherent such that the adhesive will bond metal to rubber upon heating under pressure. Various metal adherents disclosed include thermosetting phenol-aldehyde resins, polymers of ethylenically unsaturated materials, and halogenated rubber such as chlorinated natural rubber or chlorinated polychloroprene. The rubber adherent basically consists of a poly-C-nitroso compound, although various other rubber adhering components may be utilized such as vulcanizable olefins.
U.S. Pat. No. 4,139,693 discloses adhesive compositions useful for bonding metal surfaces that are prepared by mixing a monomeric ester of 2-cyanoacrylic acid with an anionic polymerization inhibitor and a carboxysubstituted trihydroxy aromatic compound.
U.S. Pat. No. 4,167,500 describes an aqueous adhesive composition that contains a water dispersible novolak phenolic resin, a methylene donor such as an acetal homopolymer or acetal copolymer, and water. The phenolic resins described are primarily derived from resorcinaol and alkylphenols such as p-nonylphenol although various other polyhydroxy phenols are mentioned, such as phloroglucinol and pyrogallol.
U.S. Pat. No. 4,195,140 describes a two-component adhesion promoting composition that contains as the first component a triglycidyl isocyanurate and a methylene donor crosslinking agent and as the second component at least one methylene acceptor selected from various monomeric monohydric alkylphenols and monomeric polyhydric phenols such as phenol, p-t-butylphenol, p-phenylphenol, o-cresol, m-cresol, resorcinol, phloroglucinol, orcinol and pyrogallol.
It has been found that many traditional adhesive compositions for adhesively bonding elastomers to metal such as those described above cannot withstand the harsh high temperature fluid and corrosive material environments currently being experienced in various automotive and industrial applications. For example, many of the currently available adhesive compositions will blister or rapidly corrode when exposed to high temperature fluids or corrosive environments. Furthermore, many of the traditional adhesive compositions require substantial metal surface preparation as discussed above prior to application of the adhesive. A need therefore exists for an elastomer-metal adhesive system that will withstand these increasingly demanding and harsh environmetal conditions and that can be applied with minimal metal surface preparation to a variety of metal surfaces contaiminated with oils, rust, dirt or the like.